Light Emitting Diodes (LEDs) are preferred over lasers for short distance fiber communications because of their greater reliability and lower cost, although the optical power coupled into a fiber is smaller. Since their emission is purely spontaneous, LEDs are less susceptible to power changes with temperature. Therefore, it is of interest to seek improvements in output intensity without resorting to a structure with optical gain.
By positioning an optical reflector behind a thick spontaneously emitting surface, the far field intensity of an LED could be doubled, compared to an LED without a mirror. For example, see T. Karo et al. "GaAs/GaAlAs Surface Emitting IR LED With Bragg Reflector Grown MOCVD", Journal Crystal Growth, 107, 1991, pp. 832-835. The normal incidence emission can also be enhanced by making the active region thin, and placing it in the anti-node of an optical mode. Deppe et al. demonstrated with a single quantum-well structure that the enhancement and inhibition of emission depends on the quantum well placement relative to a single reflective mirror. See D. G. Deppe et al., "Optically-Coupled Mirror Quantum Well InGaAs-GaAs Light-Emitting Diode", Electronic Letters, Vol. 27, 1990, pp. 1165-1166. Also see U.S. Pat. No. 5,089,860 issued Feb. 18, 1992, to Dennis G. Deppe et al. While Deppe et al., discussed the dependency of the normal incidence of emission on the position of the single quantum well structure relative to the single mirror, no quantitative consideration was given to the emission intensity of such single-mirror devices. Applicants have discovered that while the normal incidence of emission of a device with a single quantum well was enhanced due to the positioning of the quantum well in the anti-node of the optical mode of the LED, increase in an operating current beyond a certain limit led to the saturation of the emission intensity of such an LED.